Multiparameter lighting fixtures are lighting fixtures, which illustratively have two or more individually remotely adjustable parameters such as focus, color, image, position, or other light characteristics. Multiparameter lighting fixtures are widely used in the lighting industry because they facilitate significant reductions in overall lighting system size and permit dynamic changes to the final lighting effect. Applications and events in which multiparameter lighting fixtures are used to great advantage include showrooms, television lighting, stage lighting, architectural lighting, live concerts, and theme parks. Illustrative multi-parameter lighting fixtures are described in the product brochure showing the High End Systems product line for the year 2000 and are available from High End Systems, Inc. of Austin, Tex.
Multiparameter lighting fixtures are commonly constructed with a lamp housing that may pan and tilt in relation to a base housing so that light projected from the lamp housing can be remotely positioned to project on a stage surface. Commonly a plurality of multiparameter lights are controlled by an operator from a central controller. The central controller is connected to communicate with the plurality of multiparameter lights via a communication system. U.S. Pat. No. 4,392,187 titled “Computer controlled lighting system having automatically variable position, color, intensity and beam divergence” to Bornhorst, incorporated herein by reference, discloses a plurality of multiparameter lights and a central controller.
The lamp housing of the multiparameter light contains the optical components and the lamp. The lamp housing is rotatably mounted to a yoke that provides for a tilting action of the lamp housing in relation to the yoke. The lamp housing is tilted in relation to the yoke by a motor actuator system that provides remote control of the tilting action by the central controller. The yoke is rotatably connected to the base housing that provides for a panning action of the yoke in relation to the base housing. The yoke is panned in relation to the base housing by a motor actuator system that provides remote control of the panning action by the central controller.
It is desirable for a multiparameter light to have a high intensity light output and a remotely variable color system. The use of dichroic filters to color the light emitted by a multiparameter theatre lighting fixture is known in the art. U.S. Pat. No. 4,392,187 to Bornhost, discloses the use of dichroic filters in a multiparameter light. Bornhorst writes “The dichroic filters transmit light incident thereon and reflect the complement of the color of the transmitted beam. Therefore, no light is absorbed and transformed to heat as found in the prior art use of celluloid gels. The use of a relatively low power projection lamp in lights 30 and 110 substantially reduces the generation of infrared radiation which causes high power consumption and heat buildup within prior art devices.”
Bornhorst U.S. Pat. No. 4,392,187 was filed in March 1981 and since that time the use of dichroic filters to color the light emitted by a multiparameter stage light is generally practiced in the art. One thing has continued to change however. There is an on going demand within the theatre industry for ever increasing light output levels from multiparameter theater lights. Therefore, the projection lamp source for the modern day multiparameter light has been increasing in power and light output. For example while the lamp 50 disclosed by Bornhorst is a common projector lamp having a power consumption of 350 watts, there is a demand today for multiparameter lights utilizing lamps that have a power consumption of 2000 Watts and over.
Bornhorst discloses color wheels 112 and 114 that have dichroic filters mounted thereon and permit the coloring of the light emitted by a lamp 50. While the use of color wheels that support multiple wavelengths of dichroic filters to color the light of a multiparameter stage light is still in common practice, it is also common practice to construct a multiparameter light having variable density dichroic filter flags that gradually color the light using a subtractive color method. The subtractive color method may use the dichroic filter flag colors of cyan, magenta and yellow to gradually and continuously vary the color of today's multiparameter stage light producing a pleasing color fade when visualized by an audience. The gradual and continuous varying of cyan, magenta and yellow in the light path of a multiparameter light is referred to as “CMY color mixing” in the theatrical art.
U.S. Pat. No. 6,687,063 to Rasmussen discloses a dichroic color mixing filter flag system for use with a multiparameter light color mixing system. Rasmussen discloses a dichroic color mixing flag in FIGS. 8 and 12 with dichroic etched fingers that operate to produce a variable color as they are translated across the light created by the optical path.
Current state of the art dichroic color mixing flags are constructed of a low expansion borosilicate glass substrate. The low coefficient of expansion of the borosilicate glass substrate helps to provide a reasonable tolerance to thermal shock as the dichroic color mixing flag is translated or moved into and out of the high energy light created by the optical path. A low expansion borosilicate glass substrate use in the manufacture of dichroic filter flags is commercially available from Schott America, 555 Taxter Road, Elmsford, N.Y. and is referred to as Schott Borofloat.
The inventors of the present application have noticed during development of new multiparameter stage lights using lamps having a wattage of 2000 watts and over, that the dichroic color mixing flags of the present art constructed on the present art borosilicate substrate are subject to even greater thermal shock and therefore can crack when used with such high intensity light sources. One prior art way to improve the thermal (or heat) resistance of the present art dichroic color mixing flag is to construct the dichroic filter material out of a substrate with an even lower coefficient of thermal expansion than the typical borosilicate. Unfortunately, in the prior art, this improved alternate type of substrate is usually constructed from a high purity quartz, which can be very custom and be quite expensive.